A retrospective analysis of Swedish cohort data indicates that warfarin is effective enough to remain a valid alternative to novel oral anticoagulants in patients with atrial fibrillation — if that warfarin therapy is as well managed as it was in Sweden.

The cohort provided up to 5 years of medical records from 40,449 patients with nonvalvular AFib who started on warfarin between January 1, 2006 and December 31, 2011. Cohort members, 60.0% of whom were men, started the study with a mean age of 72.5 years ± a standard deviation of 10.1 years and a mean CHA2DS2-VASc score of 3.3.

Over the course of the study period, the annual incidence of all-cause mortality was 2.19% (95% confidence interval [CI], 2.07% to 2.31%) and the annual incidence of intracranial bleeding was 0.44% (95% CI, 0.39% to 0.49%).

Patients who spent less than 70% of the study time in the therapeutic range (TTR) fared worse than average. Their annual rates of any major bleeding and any thromboembolism were 3.81% (95% CI, 3.51% to 4.11%) and 4.41% (95% CI, 4.09% to 4.73%), respectively.

Among patients whose international normalized ratio (INR) varied significantly, annual rates of any major bleeding and thromboembolism were 3.04% (95% CI, 2.85% to 3.24%) and 3.48% (95% CI, 3.27% to 3.69%), respectively. For patients with individual TTRs of 70% or more, however, the level of INR variability did not alter event rates.

Patients receiving concomitant aspirin also fared worse than average. They had annual rates of any major bleeding of 3.07% (95% CI, 2.70% to 3.44%) and thromboembolism of 4.90% (95% CI, 4.43% to 5.37%). Patients with renal failure were at higher risk of intracranial bleeding (hazard ratio, 2.25; 95% CI, 1.32 to 3.82).